'Green' Bricks from 'Green' Glass

CERAM has been working on projects assessing the cost verses benefits of the use of powdered recycled container glass in brick and paver manufacture. The main aim of the projects was to fully understand the performance of powdered glass as a fluxing agent in conjunction with a variety of UK brick making raw materials.

The current climate, of increasing fuel costs, taxation on energy based "greenhouse" emissions (CCL and EU ETS), restrictions in none fuel process emissions (HF), and the increasing cost of raw material planning, development and extraction costs, have all had a significant impact upon the fundamental economics of the brick and clay tile industry in the UK. These and the stricter quality and performance based European Standards for these construction products, have all imposed new business drivers onto the industry, increasing bottom line manufacturing costs, therefore making the use of alternative raw materials more attractive and cost effective.

To put the projects into perspective, the UK brick industry is a very significant energy user, having a yearly consumption of approximately 4.06 billion kWh equivalents of natural gas, (= c. 138.7 million therms, = c. £ 37.5 million) based on 2003 energy data collected by CERAM. The adoption, in the UK, of the EU ETS in 2007 will, under current plans, impose an upper limit on a manufacturer's generation of 'process CO₂' meaning that once reached, the only option will be to buy CO₂ credits at the prevailing market price, or cease production.

It was on this basis that one project was funded through the Waste and Resources Action Programme (WRAP), in collaboration with industry project partners, Blockleys Brick Ltd, Hanson Brick Ltd and York Handmade Brick Co Ltd.

Summary of Results:

The addition of powdered glass, of particle size 80% below 80µm, at 5% and 10% levels in bricks has been seen to have significant effects on the vitrification of the bricks during the normal works firing schedule. The result of this has been an increase in compressive strength, and a reduction in water absorption. In addition to the glass particle size, clay type appears to have a very significant effect on the degree of improvement observed, and therefore the level of benefit is very much dependant on the primary raw material type.

It has been possible to replicate the physical properties of clay only bricks fired to the normal works firing schedule, whilst reducing the firing temperature and the firing time, the ultimate result of which is the reduction of energy used. The full scale works trial undertaken on the extruded, solid, Etruria Marl pavers showed a potential energy saving of up to 20%, along with an increase in throughput of 7.7% by the addition of 5% recycled powdered glass.

In addition to the energy savings, a reduction of 33% of the level of HF emission was achieved. It is thought that the generation of the glass melt at lower temperatures than normal, has resulted in the capture of the HF in the glassy ceramic matrix.

Additional benefits observed and measured during the project include a 10% reduction in electrical energy required during extrusion; enhanced quality, especially for freeze-thaw durability and the water absorption values for Class B Engineering bricks. Reduction in used energy (Natural Gas) also reduces the levels of 'process CO₂' emitted which assists the manufacturer in achieving the energy (CCL) and emission (EU ETS) related environmental legislative taxation targets.